Recently, the development of wireless communication technology has contributed to the popularization of mobile devices. In response to the development of wireless communication technology, secondary batteries are essentially used as a power supply for mobile devices. Meanwhile, electric vehicles, hybrid vehicles and the like that have been developed to prevent environmental pollution are also powered by secondary batteries.
Thus, the use of secondary batteries has been increasing in various industrial fields, and their output, capacity and structure are diversifying according to the characteristics of the industrial field in which the secondary batteries are used.
Generally, a secondary battery comprises an electrode assembly including an anode and a cathode, which are formed by applying active materials on both sides of a plate-shaped current collector, and a separator interposed between the anode and the cathode. The electrode assembly is received in a cylindrical or prismatic metal can or in a pouch-type case made of an aluminum laminate sheet together with a liquid electrolyte or a solid electrolyte. Moreover, the electrode assembly may have a structure, in which a plurality of jelly-roll type or thin plate-like unit electrodes each including sheet-shaped anode/separator/cathode are sequentially stacked, so as to increase the capacity of the secondary battery. Therefore, the electrodes (such as anode and cathode) of the electrode assembly essentially have a plate shape.
This conventional plate-shaped electrode structure has an advantage of achieving a high degree of integration during winding or stacking of the electrode assembly. However, depending on the necessity of the industrial field, it is very difficult to modify the structure of the plate-shaped electrode. Moreover, the plate-shaped electrode structure is sensitive to changes in the volume of electrodes during charging and discharging cycles. Furthermore, the gas generated in the cells is not easily discharged to the outside, which can result in problems such as high potential difference between the electrodes.
In particular, to meet the various needs of the consumers, the types of devices using secondary batteries are diversifying and the design of the devices are becoming very important. For these special types of devices to create a separate area or room so to mount secondary batteries having a conventional structure and/or shape (such as cylindrical, prismatic, or pouch type) can be considered a significant obstacle in the expansion of wireless technology or to the introduction of new designs. For example, if a newly developed device has a long and narrow space in which a secondary battery is to be mounted, it is essentially impossible or ineffective to modify the structure of the secondary battery including an electrode assembly using plate-shaped electrodes as a basis so to mount the secondary battery in the device. That is, since the conventional cylindrical, coin-type and prismatic batteries are formed to have specific shapes, they cannot freely change in shape and are limited in the use thereof. Moreover, they have a problem of not being able to bend or twist to meet their intended use.
In order to solve the above problems, the present applicant discloses “an electrode assembly of a novel structure and a secondary battery comprising the same” (filed on Jan. 17, 2006 and registered on Feb. 12, 2008 as Korean Patent No. 10-0804411), the entire contents of which are incorporated herein by reference.
However, such a secondary battery (hereinafter, referred to as a “cable-type secondary battery”) has insufficient flexibility. Moreover, in the case the cable-type secondary battery is excessively deformed by the application of an external force, the active materials may be released.